Seal monitoring and control system

ABSTRACT

A seal monitoring and control system for a gas lubricated non-contacting seal includes various sensors providing signals to a programmable logic control system. The control system is disposed to determine a presence of an anomalous operating condition of the seal, for example, based on phase, relative position of rotor to stator or other signals in combination provided by the various sensors to provide an output signal, which in one embodiment performs at least one mitigating process to correct the anomalous operating condition by adjusting at least one operating parameter of the seal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of U.S. Provisional PatentApplication No. 61/055,056, filed May 21, 2008, which is incorporatedherein in its entirety by reference.

BACKGROUND

The disclosure relates to non-contacting, gas lubricated seals forrotating components, including but not limited to conditioning andcontrol systems for such seals.

In typical applications, gas lubricated non-contacting seals aredisposed to seal a rotating interface between a shaft and housing of acompressor operating to compress a gas. During operation, a portion ofthe flow of the gas being processed may be diverted from the operatingflow and filtered to remove particulate and liquid mist that may bepresent in the operating flow. This diverted gas flow may be furtherprocessed, for example, superheated to a temperature above its dewpoint, and provided to gas lubricated non-contacting seals as anoperating fluid.

Upsets in the compression process, such as improper gas conditioning, ora change in the composition of the operating flow of gas, may causeliquid and/or solid condensates into the diverted gas flow. Suchintrusion of liquids and/or solids into a seal interface of the gaslubricated non-contacting seals can lead to reduction of operating lifeof the seal or, under extreme conditions, failure of the seal.

Non-contacting dry gas seals commonly applied to gas compressors includea seal arrangement (single, tandem, or double), gas conditioningequipment, which is often arranged in modular form, and gas supplycontrols, which are typically arranged in a control panel. Suchcombinations are employed for both overhung and beam compressors.Monitoring of seal integrity and operation is typically accomplished bymonitoring seal leakage. One can appreciate that a high rate of leakageis used as an indication that the seal has failed, which in the majorityof cases is determined after disintegration of the sealing facesrequiring an urgent shutting down of the compressor.

Moreover, one requirement for installation of dry gas seals is theability to accommodate axial movement of the compressor shaft relativeto the compressor housing during operation. A typical operatingdisplacement tolerance specification is built into the seal during thedesign stage. Typically, seal installation plates position the seal atthe nominal or optimum position within the compressor housing. Thenominal position of an installed seal may be defined by a dimensionlocating the relationship between the rotating and stationery componentsthat carry the seal components, which is sometimes referred to as the“installation reference” of a seal.

The installation reference dimension is typically measured between asurface that axially determines and secures the axial position of theseal rotor and the seal stator during operation, for example, thrustrings associated with the housing and shaft. Tolerance of axial motionof the seal during operation is needed to accommodate changes in therelative positioning between the rotating and stationary components ofthe compressor, which the seal components track. Several factors cancause changes in the relative position of a seal, such as the “as-built”condition of the equipment and thermal transients.

The “as-built” condition of a seal is a specific stack-up of tolerancesfor a given seal arrangement. To address the “as-built” condition, aseal supplier may provide an initial installed tolerance for the seal asinstalled. Accounting for this condition, a seal may be installed at a“0” position, which still leaves the fall range of the resultingdisplacement tolerance to accommodate movement within the compressorduring operation, the most significant of which typically being thermaltransients. As is known, thermal transients can change the relativeposition of a seal because the compressor rotor may expand or contractat a different rate than the compressor stator or casing due to changesin the temperature of the process fluid, which may result in adimensional relationship change between the rotor and stator sealcomponents.

BRIEF SUMMARY OF THE DISCLOSURE

The disclosure describes, in one aspect, a seal monitoring system for agas lubricated non-contacting seal disposed in sealing relationshipbetween a rotatable shaft and a housing of a compressor. The sealmonitoring system includes a phase sensor disposed to provide a phasesignal indicative of non-gaseous matter being present adjacent to thegas lubricated non-contacting seal. A programmable logic control systemis disposed to receive the phase signal and determine an operatingcondition of the gas lubricated non-contacting seal based on the phasesignal. The programmable logic controller is further disposed to providean output signal in response to the operating condition.

In another aspect, the disclosure describes a supply system forproviding a flow of treated gas to a gas lubricated non-contacting sealdisposed within a compressor. The supply system includes a controlsystem and three pluralities of sensors. A first plurality of sensorsmeasures seal operating parameters and provides a first plurality ofsignals indicative of the seal operating parameters to the controlsystem. A second plurality of sensors measures supply system operatingparameters relative to the flow of treated gas, and provides a secondplurality of signals to the control system. A third plurality of sensorsmeasures compressor operating parameters and provides a third pluralityof signals indicative of the compressor operating parameters to thecontrol system. The control system determines an operating condition ofthe gas lubricated non-contacting seal based on the first, second, andthird pluralities of signals, and provides an output in response to theoperating condition.

In yet another aspect, the disclosure describes a method of monitoringand controlling operation of a seal associated with a supply systemsupplying a flow of process gas to the seal. The method includesacquiring a plurality of sensor signals provided by a plurality ofsensors associated with the seal and the supply system. The plurality ofsensor signals is processed to determine presence of an anomalousoperating condition of said seal. A mitigation procedure that adjusts atleast one operating parameter of said seal is initiated and conductedwhile the anomalous operating condition is present and while each sensorsignal is below a corresponding threshold.

In yet another aspect, the disclosure describes a seal monitoring systemfor a gas lubricated non-contacting seal disposed in sealingrelationship between a rotatable shaft and a housing of a compressor.The seal monitoring system includes a position sensor providing aposition signal indicative of the relative axial position of rotatablecomponents and stationary components of the gas lubricatednon-contacting seal. A programmable logic control system receives theposition signal and determines an operating condition of the gaslubricated non-contacting seal based on the position signal. Theprogrammable logic controller further provides an output signal inresponse to the operating condition.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a cross section of a tandem seal arrangement having varioussensors embedded therein in accordance with the disclosure.

FIG. 2 is a block diagram of a supply system associated with acompressor in accordance with the disclosure.

FIG. 3 is a block diagram of an embodiment of a programmable logiccontroller having interconnections to various components and systems ofa seal arrangement associated with a beam compressor in accordance withthe disclosure.

FIG. 4 is a block diagram for a monitoring and control algorithm inaccordance with the disclosure.

FIG. 5 is a flowchart for a method of detecting an anomalous staticcondition of a seal in accordance with the disclosure.

FIG. 6 is a flowchart for a method of determining the presence andmitigating the effects of an anomalous operating condition in accordancewith the disclosure.

DETAILED DESCRIPTION

Non-contacting dry gas seals, such as those commonly applied to gascompressors, include a single, tandem, or double seal arrangements. In atypical installation, gas conditioning equipment is often arranged inmodular form, and gas supply controls are typically arranged in a gascontrol panel. Such combinations are employed for both overhung and beamcompressors. While one combination that includes a tandem non-contactingdry gas seal for a compressor that is part of an installation having gasconditioning equipment and gas supply controls arranged in a controlpanel is used in the description of the embodiments that follow, but onecan appreciate that the principles and methods disclosed herein areapplicable to other structural combinations, and/or seal configurations.As is well known, the associated gas control panel is arranged and pipedinto the system to control treated seal gas supplied from the processsource. It also receives gas from the leakage ports. Appropriate flowmonitoring meters are incorporated into the system at the control panel.

FIG. 1 is a partial cross section of a tandem non-contacting dry gasseal arrangement 100 disposed between a rotating compressor shaft 102and a compressor housing 104. In the view illustrated, the rotatingcompressor shaft 102 is connected to a compressor impeller (not shown)disposed in a process cavity 106 of the compressor, and is supported bythe housing 104 via a bearing (not shown) disposed in a bearing cavity108 of the housing 104. A bore 120 formed in the compressor housing 104extends between process cavity 106 and bearing cavity 108 and defines anannular seal chamber 109. A shroud or labyrinth seal 128 prevents thefree flow of gas from the process cavity 106 into the bore 120. Thelabyrinth seal 128 extends over a radially extending opening formedbetween the rotating compressor shaft 102 and the compressor housing104, to which the labyrinth seal 128 is sealed by way of a radialcompression seal 130 disposed in a channel 132 formed in the labyrinthseal 128. At its radially inner end, the labyrinth seal 128 forms aplurality of ridges 134 in close proximity to an outer surface 136 ofthe rotating compressor shaft 102. The plurality of ridges 134 and thecorresponding intermediate cavities formed between any two consecutiveridges 134 impede the ingress of gas from the process cavity 106 intothe seal chamber 109.

During operation, gas present in the process cavity 106, which can reachpressures of 6,500 PSI-G (450 BAR-G), is sealed from the bearing cavity108 and from the environment by two face seals, a first stage seal 110and a second stage seal 111, arranged in tandem. Typically thecomponents of seals 110 and 111 are preassembled into a cartridge 118which resides in the seal chamber 109. The cartridge 118 includes astator 117 associated with compressor housing 104 and a sleeve 115associated with shaft 102. Axial movement of the sleeve 115 relative tothe shaft 102 is limited by a shaft thrust ring 125 received in a groovein the shaft 102. Axial movement of the stator 117 is limited by statorthrust ring 121 received in a groove in housing 104. Assuming that theprocess gas in process cavity 106 is under pressure, all components ofthe seal arrangement 100 are urged in the direction toward thrust rings121 and 125.

The first stage seal 110 forms a first stage seal interface 112 definedbetween a first stage mating ring 114 connected to sleeve 115 disposedaround the rotating compressor shaft 102, and a first stage primary ring116 connected to the compressor housing 104 by stator 117. The secondstage seal 111 forms a second stage seal interface 122 defined between asecond stage mating ring 124 connected to the rotating compressor shaft102 by sleeve 115 and a second stage primary ring 126 connected to thehousing 104 by stator 117.

Each of the first and second stage primary rings 116 and 126 is axiallymovable along a major dimension of the bore 120 such that a controlleddistance may be maintained along each of the first and second stageseals 110 and 111. In the illustrated embodiment, a spring force isapplied to each primary ring 116 and 126 via a respective set of springs138 disposed between the seal cartridge 118 and a spring carrier 140 incontact with and corresponding to each of the first and second stageprimary rings 116 and 126.

As illustrated in FIG. 1, secondary leak paths for gases through thefirst and second stage seals 110 and 111 are blocked by radialcompression seals 142. The arrangement and materials used for theseseals can be optimized based on the application, for example, theoperating pressures of the gas, as well as the chemical composition ofthe gas and/or the operating environment of the compressor. The radialseals may include O-rings, other composite seal arrangements, such asadvanced polymer seals surrounding seal carrier members, or any otherappropriate type of seal.

Lubrication oil present in the bearing cavity 108 is prevented fromentering the seal chamber 109 of bore 120 by an oil seal, for example, aseparation seal 144. In the illustrated embodiment, the barrier seal 144is a dual-segmented carbon ring seal designed to prevent the migrationof bearing oil to the dry gas seal cartridge on turbo-compressorequipment, such as a “Type 82” or a “Type 83” seal manufactured by JohnCrane, Inc. of Morton Grove, Ill.

As discussed above, during operation, a flow of treated process gasreferred to as “sealing gas” is provided to the first stage seal 110. Aflow of barrier gas, typically an inert gas such as nitrogen (N₂), isprovided to the second stage seal 111. In the illustrated embodiment,which includes separation seal 144, a flow of separation gas is suppliedto the separation seal 144. Properly controlled flow of the sealing gas,barrier gas and separation gas through the seal elements is essential toeffective seal performance and durability.

As illustrated in FIG. 1, the labyrinth seal 128, first and second stageseals 110 and 111, and separation seal 144, divide the seal cartridge118 into a series of chambers 146, 150, 151, 160 and 164. The compressorhousing 104 similarly defines a series of annular passages 148, 154,156, 158 and 162 in communication with the chambers and passages in thestator 117 of cartridge 118. The passages 148, 154, 156, 158 and 162, inturn, are connected through ports 119 to piping, external to thecompressor housing 104, to various sources of gas or discharge conduitsas described below. Typically, this piping connects through the gascontrol panel associated with the compressor seal arrangement 100. Thegas control panel houses control valves and monitoring gauges all as iswell known an commercially available.

Chamber and passage 146 and 148 define a sealing gas inlet and receive“sealing gas” which is treated process gas usually at a pressure at orabove the process gas in the process cavity 106. This supply is treatedand controlled to ensure that moisture is removed and that it is at thedesired pressure and temperature. The sealing gas in chamber 146 blocksingress of untreated process gas from process cavity 106 acrosslabyrinth seal 108.

Chamber and passage 151 and 156 define a barrier gas inlet and receive abarrier gas input, usually nitrogen. The barrier gas is at a pressureslightly higher than the pressure of the gases in chamber and passage150 and 154. These latter passages define the sealing gas and barriergas outlet, sometimes referred to as primary leakage, usually directedto a flare for consumption of the sealing gas that passes across thefirst stage seal interface 112 and dissipation of the barrier gas thatpasses across labyrinth seal 152 from chamber and passage 151 and 156.

The barrier gas in chamber and passage 151 and 156 also passes acrosssecond stage seal interface 122 into chamber and passage 160 and 158.That gas, mostly nitrogen, exists the seal arrangement 100 as “secondaryleakage” through secondary leakage outlet defined by chamber and passage160 and 158.

A separation gas supply is delivered to the chamber and passage 164 and162 from an external source. It is usually nitrogen maintained at apressure to isolate the seal chamber 109 from oil within bearing chamber108. Some of this gas passes into the secondary leakage outlet atchamber and passage 160 and 158 across the separation seal 144.

During operation of the tandem non-contacting dry gas seal arrangement100, filtered and treated process gas diverted from the process cavity106 is provided to the sealing gas inlet passage 148 at a pressure thatis at least equal or, preferably, slightly higher than the pressure ofprocess gas in the process cavity 106. The diverted process gas may befiltered and treated in gas conditioning equipment (not shown) thatpreconditions the process gas delivered to the sealing gas inlet passage148. Such gas may be heated and/or dried to remove vapor particulatesand liquids, and in certain instances its pressure may be enhanced.

A flow of filtered and treated process gas (sealing gas) from thesealing gas inlet passage 148 enters the first chamber 146, from whereit is provided to the labyrinth seal 128 and the first stage seal 110.Due to the pressure differentials present, a portion of the flow offiltered and treated process gas may leak into the process cavity 106past the labyrinth seal 128, thus creating gas flow in a direction thatprevents unfiltered and untreated process gas from entering the firstchamber 146. A remaining portion of the flow of filtered and treatedprocess gas (sealing gas) leaks past the first stage seal 110, via a gapthat may be present along the first stage seal interface 112, and entersthe second chamber 150 and passage 154 defining the sealing gas andbarrier gas outlet.

During operation, a flow of barrier gas is provided to the barrier gasinlet passage 156 and chamber 151 at a pressure that is sufficientlyhigh to ensure flow of barrier gas from the barrier gas inlet passage156 and chamber 151 through the secondary labyrinth seal 152 intochamber 150 where it mixes with the portion of sealing gas that leaksthrough the first stage seal 110. The resulting mixture is removed fromthe seal cartridge 118 via the sealing gas and barrier gas outletpassage 154.

A portion of the barrier gas flow leaks past the second stage seal 111,via a gap along the second stage seal interface 122, and enters thesecondary leakage outlet chamber 160 and passage 158.

Barrier gas present in the chamber 160 may mix with separation gassupplied to the separation gas supply passage 162 that leaks into thesecondary leakage outlet chamber 160 past the separation seal 144. Theresulting mixture of barrier gas and separation gas in the passage 160is removed from the seal cartridge 118 via the second stage leakage andseparation gas outlet passage 158. As can be appreciated, a portion ofthe flow of separation gas from the fourth passage 164 may leak into thebearing cavity 108, thus establishing a flow direction preventing oilfrom the bearing cavity 108 from entering into the seal cartridge 118.

In accordance with the embodiment of FIG. 1, a variety of sensors isassociated with various portions of the tandem non-contacting dry gasseal arrangement 100, and the sensors are disposed to measure variousoperating parameters of the first stage seal 110, second stage seal 111,and separation seal 144. Such measurements are used to monitor anddiagnose seal integrity and operation, as well as provide early warningfor indications of anomalous seal operating conditions that may lead tofailure or damage of seal components. More specifically, the varioussensors employed are sensors providing signals to a logic controller 166that is part of a seal monitoring and control system. Such signals maybe indicative of physical parameters of the gases passing through theseal cartridge 118, such as the phase of such gases, and may also beindicative of physical parameters relating to the various components ofthe seals, such as the temperature or position of seal components withinthe seal cartridge 118. One embodiment of a set of sensors associatedwith the seal cartridge 118 in the illustrated embodiment is describedin further detail below.

As shown in FIG. 1, a first stage phase sensor 168 is disposed toprovide a first phase signal 170 to the logic controller 166. The firstphase signal 170 is indicative of the presence of liquids or solids inthe flow of filtered and treated process gas provided to the sealcartridge 118 via the sealing gas inlet passage 148. As shownschematically in FIG. 1, the first phase signal 170 is provided to thelogic controller 166 via a communication line, which is shown in dashedline. In one embodiment, the first stage phase sensor 168 may be aconductivity sensor, inductive sensor, or similar device, and mayprovide information in the form of discrete, or continuous data, whichindicates the presence or absence of any phase of matter other than agaseous phase. In the illustrated embodiment, the first stage phasesensor 168 is an optical sensor, for example, which can detect thepresence of solid or liquid aerosol solutions in a gas stream based onproperties of a light beam emitted and received by the sensor.

In a similar fashion, a second stage phase sensor 172 is disposed toprovide a second phase signal 174 based on the state of matter in thefirst stage or sealing gas leakage and barrier gas outlet passage 154,and a separation-stage phase sensor 176 is disposed to provide a thirdphase signal 178 that is indicative of the presence of a liquid,typically oil from the bearing cavity 108, in the second leakage andseparation gas outlet passage 158. As with the first phase signal 170,each of the second and third phase signals 174 and 178 is provided tothe logic controller 166 via appropriate communication lines in the formof a discrete value (e.g., a value of 0 indicating a gaseous phase, anda value of 1 indicating the presence of a liquid or solid phase) oranother type of value.

Though illustrated as incorporated in the passages defined by the sealassembly stator 117 or the compressor housing 104, it is contemplatedthat the sensors 168, 172, and 176 could be located in any suitablelocation where phase recognition would be accomplished. These sensorscould, for example, be located in the piping to the associated controlpanel or within conduits of the control panel itself.

In addition to sensors providing information on the phase of the workingfluids within the seal cartridge 118, other sensors are illustrated inthe embodiment of FIG. 1 that provide information about the operatingconditions of various seal components. More specifically, a first stageprimary ring temperature sensor 180 is disposed in the seal cartridge118 and arranged to sense a temperature of the first stage primary ring116. The first stage primary ring temperature sensor 180 is disposed toprovide a first stage seal temperature signal 182 to the logiccontroller 166 via an appropriate communication line. In one embodiment,the first stage seal temperature signal 182 is an analog signal thatprovides instantaneous temperature readings to the logic controller 166in a continuous data stream. The first stage primary ring temperaturesensor 180 may be any appropriate type of sensor, including a resistivetemperature device (RTD), thermocouple, or others.

In a similar fashion, a second stage primary ring temperature sensor 184is disposed in the seal cartridge 118 and arranged to sense atemperature of the second stage primary ring 126 and provide a secondstage temperature signal 186 to the logic controller 166. As with thefirst stage primary ring temperature sensor 180, the second stageprimary ring temperature sensor 184 is an analog signal that providesinstantaneous temperature readings to the logic controller 166 in acontinuous data stream, and may include a RTD or thermocouple. Eventhough the two sensors 180 and 184 are shown associated with the primaryrings 116 and 126 of, respectively, the first stage seal 110 and thesecond stage seal 111, such sensors may be associated with thecorresponding mating rings 114 and 124 of the first and second stageseals 110 and 111 or, alternatively, any other component associated witheach seal and having a temperature that can be correlated to thetemperature of either the first stage and/or secondary rings of thefirst and second stage seals 110 and 111.

The distance or gap along the first and second stage seal interfaces 112and 122 is not only important during service, but is also important asan indication of a structural fault in a seal even when the associatedcomponent is not operative. For example, in the absence of gas pressureat the seals, the presence of a gap along the first and second stageseal interfaces 112 and 122 may be an indication that the primary ringis not aligned with the corresponding mating ring of the seal.Accordingly, information on the position of each primary ring in atandem seal arrangement, as illustrated in FIG. 1 or, in general,information about the gap along the first and second stage sealinterfaces 112 and 122 becomes relevant to an early diagnosis of a sealfailure.

In the illustrated embodiment, a first stage primary ring position or afirst stage seal gap sensor 188 is mounted to the first stage primaryring 116 and disposed to measure the gap along the first stage sealinterface 112 or, alternatively, measure a position of the first stageseal primary ring 116 relative to the first stage mating ring 114 as anindication of the gap along the first stage seal interface 112. The gapsensor 188 may provide a first stage seal gap signal 190 to the logiccontroller 166. The first stage seal gap signal 190 is indicative of thedistance or gap present along the first stage seal interface 112 in realtime and both during operation of the compressor as well as during timeswhen the compressor is not operating and there is no working gasprovided to the first stage seal 110.

A second stage primary ring position or second stage seal gap sensor 192is disposed to measure the gap along the second stage seal interface122. The second stage seal gap sensor 192 is disposed to provide asecond stage seal gap signal 194 to the logic controller 166 that isindicative of the instantaneous distance or gap separating the secondstage primary ring 126 from the second stage mating ring 124. Each ofthe first stage seal gap sensor 188 and the second stage seal gap sensor192 may be any appropriate type of proximity sensor, for example, aconductivity sensor, an inductive or variable reluctance sensor, orothers.

In the embodiment of FIG. 1, position sensor 196 is installed in theseal cartridge 118 and disposed to measure a distance indicative of theposition of rotating components of the compressor relative to theposition of the stator components. That directive is denoted as “A” inFIG. 1. As can be appreciated, stationary components of the compressorcomprise the compressor housing 104, the stator 117 of seal cartridge118, the first and second stage primary rings 116 and 126, the sealthrust ring 121, and associated non-rotating elements. The rotatingcomponents comprise the compressor shaft 102, sleeve 115, shaft thrustring 125, first and second stage mating rings 114 and 124, andassociated rotating elements.

The position sensor 196 is disposed to provide a position signal 198 tothe logic controller 166. The position signal 198 indicates the axialdistance, or change in axial distance during operation, of the rotatingcomponents of the compressor and seal relative to the stator component.In other words, the position signal 198 may be used to track the axialmovement of the rotating components of the seal and compressor relativeto the stationary components. Moreover, the position sensor 196 may beused during installation of the seal to confirm the relevant “as-built”and/or “as installed” positions of the seal cartridge 118, as well asmonitor changes in their position during operation of the compressor.When monitoring such parameters, the position signal can be used providean output, for example, to trigger an alert, when the initial “as-built”and/or “as-installed” displacement exceeds a maximum allowableinstallation tolerance or when the total displacement approaches a totalmaximum allowable operational tolerance.

A simplified schematic of a supply and treatment system 200 forproviding filtered and treated sealing gas to non-contacting dry gasseals is shown in FIG. 2. In the illustrated embodiment, the supply andtreatment system 200 is associated with a compressor 202 having at leastone assembly comprising two non-contacting dry gas seals arranged intandem, for example, the first stage seal 110 and the second stage seal111 (as shown in FIG. 1), as well as a separation seal, for example, theseparation seal 144 (FIG. 1). The compressor 202 operates to compress aflow of process gas that is provided to the compressor 202 via a processgas inlet passage 204. Compressed gas exits compressor 202 at acompressed process gas discharge conduit 206.

The housing of compressor 202 includes various inlets and outlet ports,associated with a dry gas seal assembly operating within the compressor202 as previously described relative to FIG. 1. More specifically, andin reference to FIG. 1 and FIG. 2, the compressor 202 includes a sealinggas or process gas inlet conduit 208 fluidly connected to the sealinggas inlet passage 148, and a sealing gas and barrier gas outlet conduit210 fluidly connected to the sealing gas and barrier gas outlet passage154. The compressor further includes a barrier gas inlet conduit 212fluidly connected to the barrier gas inlet passage 156, and a barriergas and separation gas outlet conduit 214 fluidly connected to thesecondary leakage or barrier gas and separation gas outlet passage 158.The compressor 202 also includes a separation gas inlet conduit 216fluidly connected to the separation gas supply passage 162 and mayinclude an optional separation gas outlet conduit 218 fluidly connectedto the bearing cavity 108 of the compressor 202 and arranged to ventseparation gas leaking past the barrier seal 144 into the bearing cavity108.

As described, the various inlet and outlet conduits connected to thehousing of the compressor 202 define flow circuits for gas essential tooperation of the dry gas seals in the compressor 202. As can beappreciated, the illustrated embodiment is provided consistent with theembodiment of a dry gas tandem seal arrangement as shown in FIG. 1,which means that other seal arrangements may have more or fewer inletand outlet conduits formed in the compressor as appropriate to supplygas to dry gas seals operating therein. It should also be noted that thedepiction of the location of the various sensors described withreference to FIGS. 1 and 3 is for illustrative purposes. The describedsensors may be disposed in alternative locations within the fluidcircuitry providing for flow of seal gases to and from a sealarrangement without departing from the invention. Moreover, it iscontemplated that any given dry gas seal installation may include all,or less than all, of the specific sensors and parameter monitoringcomponents illustrated herein. These descriptions are merelyillustrative of available options.

In reference now to FIG. 2, the process gas supplied to the sealing gasor process gas inlet conduit 208 is, in one embodiment, process gasdiverted from the compressed process gas conduit 206. As shown in FIG.2, a process gas supply branch 220 extends from the compressed processgas conduit 206 and includes a process gas control valve 222 that metersthe flow of compressed process entering a process gas treatment module224 in response to a valve control signal 223. The process gas treatmentmodule 224, which is shown surrounded by dashed lines, is arranged tofilter and adjust the physical properties of process gas supplied tooperate the first stage seal of the compressor 202, as well as adjustthe pressure of the sealing gas. More specifically, the process gastreatment module 224 includes an intensifier 225 operating to adjust thepressure of process gas in response to a process gas pressure adjustmentsignal 227, and an auxiliary process gas supply reservoir 226 that canstore process gas under pressure Gas from the auxiliary process gassupply reservoir may be used to augment the flow of process gas providedto the sealing gas inlet conduit 208 by selective activation of anauxiliary process gas control valve 228 in response to an auxiliaryvalve control signal 229.

The physical properties of process gas entering the process gastreatment module 224 are measured by a pressure sensor 230, which isdisposed to provide a pressure signal 231 of process gas pressureentering the treatment module 224, and a temperature sensor 232, whichis disposed to provide a temperature signal 233 indicative of thetemperature of process gas entering the treatment module 224.

In a first process, liquid or solid constituents of the process gas flowentering the treatment module are removed, for example, by passing theflow through one or more coalescing filters 234. One example of aninstallation using coalescing filters is shown and described in U.S.Pat. No. 6,715,985, titled “Gas Conditioning System,” which was grantedon Apr. 6, 2004, is assigned on its face to John Crane Inc. of MortonGrove, Ill., (hereafter, the '985 patent), and which is incorporatedherein in its entirety by reference. A delta-P sensor 236 is disposed tomeasure a pressure difference across the coalescing filters 234 andprovide a pressure difference signal 237 indicative of the extent offilter saturation.

A phase sensor 238 is disposed to sense the presence of solids and/orliquids in the flow of process gas exiting the coalescing filters 234,and provide a process gas phase signal 239 indicating the presence of aphase of matter in the flow of process gas that is not gaseous. In oneembodiment, the phase sensor 238 may be a conductivity sensor, inductivesensor, or similar device, and may provide the phase signal 239 in theform of discrete data, for example, a value of 0 when gas is sensed anda value of 1 when a solid or liquid matter phase is detected.

The treatment module 224 further includes a process gas heater/cooler240 disposed to selectively change the temperature of the flow ofprocess gas passing through the treatment module 224 in response to atemperature change command signal 241. During operation, the process gasheater/cooler 240 may adjust the temperature of the process gas undervarious conditions, for example, to cool the gas at times of elevatedseal temperature within the compressor, or to heat the gas at times whenliquids requiring evaporation are sensed in the process gas.

A flow control device 242 is disposed to control the rate of flow ofprocess gas supplied to dry gas seals of a compressor. The flow controldevice 242 may be a simple valve or may alternatively be a deviceproviding a fine control of a gas flow passing therethrough, such as adevice that regulates the volume of gas delivered therethrough bymaintaining a constant pressure differential across a metering orifice.Regardless of its configuration, the flow control device 242 can be anydevice capable of providing a controlled flow of process gas in responseto a flow control signal 243.

In the illustrated embodiment, an additional temperature sensor 244providing a sealing gas temperature 245, and a flow sensor 246 providinga sealing gas flow rate 247, are disposed downstream of the flow controldevice 242 within the treatment module 224. The sealing gas temperature245 and sealing gas flow rate 247 are indicative of the temperature andflow rate of process gas entering the seal arrangement of compressor 202during operation.

The various sensor and command signals associated with the treatmentmodule 224 are exchanged between the various sensors and actuators ofthe treatment module and a seal monitoring and control system via atreatment module communication line 250, which is shown as a singledotted line but which is intended to include any appropriate number ofcommunication lines or communication channels enabling the exchange ofinformation and command signals between a controller included within theseal monitoring and control system 248, for example, the logiccontroller 166 shown in FIG. 1, and the various sensors and controldevices included within the treatment module 224.

In the embodiment illustrated, a compressor communication line 252 isdisposed to provide a channel of communication between various sensorsassociated with compressor components, such as the sensors shown anddescribed relative to FIG. 1. The compressor communication line 252 iscapable of providing various channels or of communication that provideinformation from each of the sensors associated with the compressor 202to the seal monitoring and control system 248. In one embodiment, thecompressor communication line 252 may be further associated with aplurality of sensors associated with the compressor and disposed tomeasure operating parameters thereof, such as compressor speed, suctionpressure, discharge pressure, vibration, and so forth. Such additionalparameters may be provided to the seal monitoring and control system 248via the compressor communication line 252.

The gas supply and treatment system 200 further includes a barrier gasand separation gas supply system 254, which is shown surrounded bydashed lines in FIG. 2. In one embodiment, a single type of gas may beprovided as a separation gas to a second stage dry gas seal and to aseparation seal, for example, nitrogen, but different gases may also beused. In the illustrated embodiment, gas is provided to the barrier gasand separation gas supply system 254 from a storage tank 256. The gasfrom the storage tank 256 may be treated by a filter 258. Operation ofthe filter 258 may be monitored by measurement of a pressure differenceacross the filter 258 by a delta-P sensor 260 providing a pressuredifference signal 262. The pressure of gas in the storage tank 256 maybe measured by a pressure sensor 264 providing a storage pressure signal266.

A flow of filtered gas exiting the filter 258 passes through a conduit268 before being selectively distributed into the separation gas inletconduit 212 and the barrier gas inlet conduit 216. In one embodiment, aseparation gas control valve 270 diverts a portion of the gas from theconduit 268 into the separation gas inlet conduit 212 in response to aseparation gas valve control signal 271 provided by the seal monitoringand control system 248. Similarly, a barrier gas control valve 272diverts a remaining portion of the gas from the conduit 268 into thebarrier gas inlet conduit 216 in response to a barrier gas valve controlsignal 273.

Various sensors are disposed to provide measurement signals indicativeof the pressure, flow rate, and phase of gas in each of the separationgas and barrier gas inlet conduits 212 and 216. More specifically, aseparation gas flow sensor 274 provides a separation gas inlet flowsignal 275, a separation gas phase sensor 276 provides a separation gasphase signal 277, and a separation gas inlet pressure sensor 278provides a separation gas inlet pressure signal 279. Similarly, abarrier gas flow sensor 280 provides a barrier gas inlet flow signal281, a barrier gas phase sensor 282 provides a barrier gas phase signal283, and a barrier gas inlet pressure sensor 284 provides a barrier gasinlet pressure signal 285.

The various sensor and command signals associated with the barrier gasand separation gas supply system 254 are exchanged between the varioussensors and actuators and the seal monitoring and control system 248 viaa communication line 286, which is shown as a single, dotted line butwhich is intended to include any appropriate number of communicationlines or communication channels enabling the exchange of information andcommand signals between a controller included within the seal monitoringand control system 248, for example, the logic controller 166 shown inFIG. 1, and the various sensors and control devices included within thebarrier gas and separation gas supply system 254.

The supply and treatment system 200 further includes flow sensorsmeasuring the flow rate of seal gases exiting the seal arrangement suchas seal arrangement 100 of FIG. 1 of compressor 202 during operation.More specifically, a process and barrier gas leakage flow sensor 288 isdisposed along the process and barrier gas outlet conduit 210 andmeasures, for example, in reference to the arrangement shown in FIG. 1,the flow rate of the mixture of process gas leaking past the first stageseal 110 and of barrier gas leaking past the secondary labyrinth seal152. The process and barrier gas leakage flow sensor 288 provides afirst stage seal leakage signal 289 to the seal monitoring and controlsystem 248.

In a similar fashion, a barrier and separation gas leakage flow sensor290 is disposed along the barrier and separation gas outlet conduit 214.The barrier and separation gas leakage flow sensor 290 provides a secondstage seal leakage signal 291 indicative of the flow rate of gas leakingpast the second stage seal 111 and the separation seal 144 to the sealmonitoring and control system 248. Finally, an optional bearing cavityleakage flow sensor 292 provides a bearing cavity gas leakage signal 293indicative of the flow rate of barrier gas leaking into the bearingcavity 108 (FIG. 1) past the separation seal 144 (FIG. 1), which exitsthe compressor 202 via the optional separation gas outlet conduit 218.As with the other leakage signals, the bearing cavity gas leakage signal293 is provided to the seal monitoring and control system 248.

A block diagram of a system schematic for an illustrated installation ofa system 300 of an overhung compressor is shown in FIG. 3. In thediscussion relative to FIG. 3, components or systems that are the sameor similar to components and systems previously described are denoted bythe same reference numerals as previously used for simplicity. Whilespecific sensors are illustrated and described in connection with FIG.3, it is understood that alternative combinations of parametermonitoring could be employed. For example, as illustrated in FIG. 1, theseal arrangement could include gap sensors, such as the gap sensors 188and 192 that provide first stage seal gap signal 190 and second stageseal gap signal 194.

As shown in FIG. 3, a prime mover 302 provides power to operate anoverhung compressor 304 via drive shaft 306. The drive shaft 306includes a first stage seal 308 and a secondary seal 310 in a tandemconfiguration. Each of the first stage and secondary seals 308 and 310is a dry gas seal and is essentially associated with sensors providingsignals indicative of the gas or seal temperature, the presence ofliquid in the gas stream provided to each seal, and of the positionbetween sealing elements and the rotor and stator. More specifically,the first stage seal 308 includes a temperature sensor 312 providing afirst stage seal temperature signal 313 and a first stage seal phasesensor 314 providing a first stage seal phase signal 315. The secondaryseal 310 includes a temperature sensor 318 providing a secondary sealtemperature signal 319, a secondary seal phase sensor 320 providing asecondary seal phase signal 321, and a secondary seal position sensor322 providing a secondary seal position signal 323.

The various sensor signals from the first stage and secondary seals 308and 310 are provided to a programmable logic controller 324 viaappropriate signal communication lines. Such signal communication linesmay be lines communicating analog and/or digital signals, and mayinclude one or more electrical conduits relaying information in a singleor multiple channels. In one embodiment, the signal communication linesmay be channels belonging to a local area network (LAN) arrangementdisposed to provide communication of signals and commands between theprogrammable logic controller 324 and other components, actuators,and/or systems.

In the illustrated embodiment, the programmable logic controller 324 isshown as a single component, but in alternate embodiments the logicfunctions provided by such a device may include more than one controllerdisposed to control various functions and/or features of a system. Forexample, a master controller, used to control the overall operation andfunction of the system, may be cooperatively implemented with secondarycontrollers dedicated to monitor and control separate sub-systems. Inthis embodiment, the term “controller” is meant to include one, two, ormore controllers that may be associated with the system 300 and that maycooperate in controlling various functions and operations of the system300. The functionality of the controller, while shown conceptually inFIG. 3 to include various discrete functions for illustrative purposesonly, may be implemented in hardware and/or software without regard tothe discrete functionality shown. Accordingly, various interfaces of thecontroller are described relative to components of the system 300 shownin the block diagram of FIG. 3. Such interfaces are not intended tolimit the type and number of components that are connected, nor thenumber of controllers described.

In the embodiment illustrated in FIG. 3, the programmable logiccontroller 324 cooperates with a memory device 326 and with an outputcircuit driver 328. The memory device 326 may include areas of read-onlymemory (ROM), programmable read-only memory (PROM), random-access memory(RAM), and others, which can store operational programs, constants,service logs, and other parameters relevant to the operation of theprogrammable logic controller 324 and of the system 300. The outputcircuit driver 328 is a device that provides appropriate command signalsto various actuators in the system 300, such as gas control valves,bypass valves, heaters, pressure intensifiers, and so forth. The outputcircuit driver 328 may include circuits that receive, transform, and/orinterpret commands from the programmable logic controller 324 intocommand signals that are useable in effecting a change in the operatingcondition of a component. Accordingly, the output circuit driver 328 mayinclude a power supply (not shown), rectifier circuits, invertercircuits, digital to analog converter circuits, and/or any other circuitthat may be useful in controlling a system component based on a commandfrom the programmable logic controller 324.

The system 300 includes two major functional centers for servicing theoperation of the compressor 304. The first functional center is a gastreatment module 330, which is similar in certain respects to theprocess gas treatment module 224 shown in FIG. 2. The treatment module300 includes various devices that condition and treat a flow of gas 332that is provided to the first stage seal 308. The treatment module 330of the illustrated embodiment includes a coalescor 334 operating inresponse to a coalescor signal 335 provided by the programmable logiccontroller 324 via the output circuit driver 328. The coalescor 334 maybe any appropriate type of device that removes solid or liquidinclusions from a gas stream, for example, a filter, membrane,centrifugal separator, and so forth.

The gas treatment module 330 further includes a knockout filter ordemister 336, which operates in response to a demister signal 337. Thedemister 336 may be any appropriate device capable of removing aerosolsolutions or other types of moisture and/or vapors from a gas stream. Aheater 338 operating to increase and/or decrease the temperature of theflow of gas 332 operates in response to a heater signal 339. The heater338 may be any appropriate type of heat exchanger operating to impart orremove heat from the flow of gas 332 being treated. Finally, anintensifier 340 operating in response to an intensification signal 341operates to adjust the pressure of the flow of gas 332. One canappreciate that other, additional, or fewer devices may be used withinthe treatment module 330 than the ones described relative to theillustrated embodiment.

A flow of treated first stage seal gas 342 exiting the treatment module330 is provided to a gas control panel 344. A flow of secondary seal gas346 may optionally provide sealing gas for the secondary seal 310. Thegas control panel 344 may include various components and subsystemsoperating to regulate or otherwise control the flow of gas to the dryseals operating within the compressor 304 based on one or more operatingparameters of the system 300. In the illustrated embodiment, the gascontrol panel 344 includes a first stage seal gas controller 348 thatregulates the flow of first stage seal supply gas, and a secondary sealgas controller 352 regulating the flow of secondary seal supply gas. Thefirst stage and secondary seal gas controllers 348 and 352 regulatetheir corresponding gas flows in response to, respectively, a firststage seal supply gas signal 349 and a secondary seal supply gas signal353 provided by the programmable logic controller 324 via the outputcircuit driver 328. In one embodiment, each of the first stage andsecond stage seal gas controllers 348 and 352 includes a flow controldevice, such as the flow control device 242 shown in FIG. 2.

A resultant flow of first stage seal supply gas 350 and secondary sealsupply gas 354 exit the gas control panel 344 and are provided to thefirst stage and secondary seals 308 and 310. The first stage and/orsecondary seal gas signals 349 and 353 responsible for adjusting theresultant flows of first stage and secondary seal supply gas 350 and 354are determined in the programmable logic controller 324 based onoperational programs processed therein. Execution of such operationalprograms involves calculation of the flow rate and physical parametersof the first stage seal gas that will yield optimal operating conditionsof the first stage seal 308, both in terms of sealing effectiveness aswell as for seal longevity.

In one embodiment, the gas control panel further includes controllersoperating to supply gas flows to other seals in the compressor 304and/or monitor the operation of the various seals. Specifically, whenthe compressor 304 includes a barrier seal, for example, the barrierseal 144 shown in FIG. 1, the gas control panel 344 includes a barrierseal gas supply controller 356 operating to provide a flow of gas to thebarrier seal, in this case, a portion of the flow of the secondary sealgas 346 entering the gas control panel 344, but other sources or typesof gas may be used.

In the illustrated embodiment, the gas control panel further includestwo seal monitors, a first stage seal monitor 358 and a secondary sealmonitor 360. Each of the first stage and secondary seal monitors 358 and360 is arranged to provide one or more outputs, for example, alarms, atincreasing levels, when various faults or malfunctions are detectedbased on the various sensor signals provided to the programmable logiccontroller 324. In addition to the sensors already described, additionalsensors may provide information to the programmable logic controllerindicative of the operating state of the compressor 304 via amulti-channel communication line 362. In the illustrated embodiment,such additional plurality of sensors may include compressor speed,suction and discharge pressure, temperature of the process gas, axialvibration of the compressor, suction and discharge compressor flangeradial vibration in each of two orthogonal directions, and, potentially,other sensors.

In general, various control algorithms operating within the programmablelogic controller 324 are arranged to provide useful functionality thatcan warn an operator of potential anomalous operating conditions, alertthe operator of fault conditions detected, as well as mitigate oraddress anomalous operating conditions occurring during operation of thecompressor 304 such that the effects of a failure can be minimized or afailure may be averted without intervention by the operator. Variousexamples of such control algorithms are presented and various methods ofoperating and monitoring dry gas seals in a compressor are describedbelow.

A block diagram for a control algorithm 400 operating within theprogrammable logic controller 324 shown in FIG. 3 is presented in FIG.4. The control algorithm 400 is arranged to monitor and adjust theoperating parameters of the first stage and/or secondary seals 308 and310 to ensure optimal operation and service life. One can appreciatethat the control algorithm 400 can be applied with equal effectivenessto the tandem seal arrangement shown in FIG. 1 by appropriateintegration thereof into the logic controller 166. In the descriptionthat follows, the control algorithm 400 is described specifically forfunctionality relative to the first stage seal 110 (shown as 308 in FIG.3), but the same or similar algorithm would be applicable to themonitoring and control of the second stage seal 111 (shown as 310 inFIG. 3) or any seal used alone or in combination with other seals.

As shown in FIG. 4, the control algorithm 400 is disposed to receivevarious signals indicative of various operating parameters. Withreference to FIG. 1, FIG. 2, and FIG. 3, the various signals generatedby sensors in the tandem non-contacting dry gas seal arrangement 100 areprovided to the control algorithm 400. Specifically, the first stagephase signal 170, the first stage seal temperature signal 182, and thefirst stage seal gap signal 190, are provided as inputs to the controlalgorithm 400. Other signals are further provided to the controlalgorithm 400 that are indicative of system operating parameters. In theillustrated embodiment, the sealing gas temperature 245, the sealing gasflow rate 247, and the first stage seal leakage signal 289 are providedas inputs. Different, additional, or fewer inputs than the onesdescribed thus far may be provided to a control algorithm that is thesame or similar to the control algorithm 400. During operation, thecontrol algorithm 400 operates to provide one or more outputs, forexample, generate alerts to an operator, in response to a determinationof presence of an anomalous condition based on the provided signals.Moreover, the control algorithm 400 includes functionality toautomatically mitigate the effects of a malfunction by adjusting variousoperating parameters of the system.

More specifically, the first stage seal temperature signal 182 isprovided to a temperature threshold comparator 402, which is a functionor other algorithm operating to compare the temperature of the firststage seal with a predetermined acceptable temperature range 404provided by the memory device 326 (also shown in FIG. 3). When the firststage seal temperature signal 182 is determined to be outside of therange 404, an appropriate output is provided in response to suchdetermination, in this case, an unexpected seal temperature alert 406 isactivated. The unexpected seal temperature alert 406, when active, mayinclude a change in a software variable indicating that a fault hasoccurred, and/or may alternatively trigger a visual and/or audibleindication to an operator by way of flashing lights, sirens, and/orother perceptible signals intended to draw the operator's attention.Instances giving rise to activation of the unexpected seal temperaturealert 406 include operating conditions when the temperature of the firststage seal 110 is above an expected value, indicating that the seal isundergoing heating due to friction or an other cause, and also includeconditions when the temperature of the first stage seal 110 is below anexpected value, which may be an indication of excessive sealing gasleakage or any other cause. In one embodiment, an additional uppertemperature threshold is used to generate a shutdown signal when thetemperature of the first stage seal 110 is determined to be in excess ofthe upper temperature threshold, for example, 500 degF (260 degC).

In the illustrated embodiment, the first stage seal temperature signal182 is further compared to the sealing gas temperature 245 in atemperature comparator 408. The temperature comparator 408 monitors thetemperature of the first stage seal 110 relative to the temperature ofthe sealing gas being provided thereto to ensure that the two are withinan acceptable range of each other after steady state operation has beenestablished. A temperature warning 410 is activated to indicate that anunexpected change has been detected when the temperature of the firststage seal 110 is determined to diverge from the temperature of thesealing gas beyond a certain extent. The temperature warning 410 isgenerally an output signal provided in response to detection of anabnormal condition.

The memory device 326 also provides expected or acceptable thresholdranges to comparators monitoring the first stage seal gap signal 190 andthe first stage seal leakage signal 289. Specifically, the first stageseal leakage signal 289 is compared to a leakage threshold range 412 ina leakage comparator 414. When the leakage is determined to be outsideof the leakage threshold range 412, indicating that the flow of gas inthe sealing and barrier gas outlet conduit 210 (FIG. 2) is below orabove the expected range, a leakage warning or alert 416 is activated toinform the operator of the anomalous operating condition. In a similarmanner, the first stage seal gap signal 190 is compared to a gapthreshold range 418 in a gap threshold comparator 420, which activates aseal gap alert 422 to indicate that the seal is operating outside ofexpected operating conditions.

One can appreciate that the various threshold ranges provided by thememory device are parameters that can be predetermined and preprogrammedinto the memory device 326. In one embodiment, the various thresholdranges are not constants, but are variable values that are determinedbased on other operating parameters of a system, such as compressorspeed, process gas composition, flow rate, and so forth. Accordingly,the gap threshold range 418 may be set to zero when the rotational speedof the compressor (not shown) is low or zero, and may be adjustedaccordingly based on the compressor speed, the density of the processgas, the temperature of the process gas, and/or other parameters duringoperation.

The control algorithm 400 is further disposed to activate a warning oralarm 424 when the presence of solids or liquids is indicated by way ofthe first phase signal 170. As discussed above, the first phase signal170 is a signal indicative of the presence of matter in a non-gaseousphase within the stream of sealing gas in or around the first stage seal110. Even though various filters and other devices are disposed toremove liquids and/or solids from the sealing gas flow, for example, thecoalescing filter 234 shown in FIG. 2, or the coalescor 334 and demister336 shown in FIG. 3, there exist operating conditions that may yieldliquid and/or solid condensates within the sealing gas flow.Accordingly, a phase determinator 426 is disposed to monitor the firstphase signal 170 and activate the alarm 424 when a non gaseous phase isdetected.

The control algorithm 400 further includes functionality to mitigateeffects of anomalous operating conditions. One example of suchmitigation functionality is provided for conditions when liquid or solidcondensates are detected in a sealing gas flow. The mitigation is aprocess of steps automatically followed by the control algorithm 400that are known to rectify the anomalous condition by removing thecondensates. In one embodiment, activation of the alarm 424 causes achange in a heater/cooler control module 428, which adjusts the heatersignal 339 provided to the heater 338 as shown in FIG. 3. In the casewhen liquids are detected, for example, such adjustment may be arrangedto cause the heater 338 to increase the temperature of the treated firststage seal gas 342 such that any liquid condensates can evaporate or anysolid condensates can sublime into the gaseous phase. Such increase ofgas temperature may continue incrementally until a maximum allowedtemperature increase has been instructed or until the first phase signal170 indicates that the liquids or solids have been removed. In specificinstances, for example, in the case when the control algorithm 400 isapplied to the second stage seal 111, and additional mitigation step maybe performed. Such additional mitigation step includes instructing aflow control module 430 providing the flow control signal 243 to theflow control device 242, as shown in FIG. 2, to increase to the rate offlow of sealing gas to the first stage seal 110. Such adjustment mayoccur in addition to the temperature increase of the sealing gasprovided to the first stage seal.

The control algorithm 400 is one example of the various algorithms thatmay be executed within the programmable logic controller 324. Thecontrol algorithm 400 and other algorithms is capable of storing andretrieving information, calculating various parameters, estimating therate of change of parameters, and performing mathematical calculationswhen determining appropriate adjustments to control signals provided tothe various components of the system. In the flowcharts that follow,various functionalities of the programmable logic controller 324 andassociated components are described. The methodologies for controlling acompressor described below are intended to be implemented viaappropriate control algorithms operating within logic controllers.

A flowchart for determining whether to prevent the initiation ofoperation of a compressor based on parameters provided from varioussensors associated with a system connected to the compressor, especiallyregarding the state of the various compressor seals associated with thecompressor, is shown in FIG. 5. In accordance with the method, a controlsystem performs various checks before enabling operation of a compressoror the system. Accordingly, a determination at 502 is performed todetermine whether liquid is present at the first stage seal, forexample, by interrogating the first phase signal 170 (FIG. 1). Whenliquid is present, a second interrogation occurs at 504 of whetherliquid is present in the supply system for process gas flow to theprimary seal, for example, as indicated by the process gas phase signal239. The control system may incrementally heat the process gas supplytemperature and incrementally increase the flow rate at 506 when noliquid is present at the seal but no liquid is detected in the supplysystem until a maximum temperature is reached at 508, at which point anoutput is provided, for example, an alarm is sounded at 510, or untilthe liquid is no longer present. When liquid is also present in thesupply system at 504, a similar intervention of increasing flow andtemperature of the process gas occurs at 512, which continues untilliquid is no longer present in the supply system, under the presumptionthat liquid in the first stage seal was liquid carried to the firststage seal from the supply system, or until the maximum temperature ofprocess gas is reached at 513. Under such circumstances, the alarm oranother output signal is activated at 510 and the system startup islocked.

The method further includes a determination of whether liquid is presentat the second stage seal, for example, by interrogating the second phasesignal 174 (FIG. 1) and the barrier gas phase signal 277 (FIG. 2) at514. When it is determined that liquid is present, an alert is activatedat 516 and system startup is locked at 518. In a similar fashion, themethod ensures that no oil has intruded past the separation seal 144(FIG. 1) and entered the third passage 160 (FIG. 1). Accordingly, thethird phase signal 178 (FIG. 1) is interrogated at 520 and theseparation gas flow is increased in the separation gas inlet conduit 216(FIG. 2) by, for example, commanding an additional opening of theseparation gas control valve 272 (FIG. 2), at 522, when it is determinedthat liquid is present. Such increase of separation gas flow continuesto incrementally augment flow as long as liquid is still present at theseparation gas outlet passage 158 (FIG. 1) or until the separation gaspressure has reached a maximum value, at 526, as indicated, for example,by the separation gas inlet pressure signal 285 (FIG. 2). Should thepresence of liquid persist when the maximum pressure has been reached at526, the startup of the system is locked at 518.

The method further includes a determination of the mechanical conditionof the first and second stage seals 110 and 111 (FIG. 1) prior tostartup. As discussed above, the primary and mating rings of both sealsare expected to be in contact when no sealing gas flow is provided andwhen the compressor is not operating. An indication of compressoroperation is considered at 528, for example, by determining whether theshaft speed of the compressor is zero and/or by comparing the inlet andoutlet pressures of the compressor and expecting them to be equal. Whenthe compressor is not yet operating, the gap or distance between eachseal is interrogated at 530, and an alarm is activated at 532 if atleast one gap is found to be non-zero. In one embodiment, the gapsignals indicative of contact between the primary and mating rings inthe first and second stage seals 110 and 111 (FIG. 1) are provided by,respectively, the first stage seal gap signal 190 and the second stageseal gap signal 194. In one embodiment, activation of the alarm at 532indicating that a mechanical malfunction may be present in the sealscauses the startup of the system to be locked at 518.

In addition to performing various checks before a compressor is placedin service, the programmable logic controller 324 (FIG. 3) is furthercapable of monitoring for anomalous operating conditions of the seal,mitigating or correcting anomalous operating conditions as they occurand while the compressor is in service, activating alerts and/orwarnings and/or other output signals when fault conditions are presentthat cannot be mitigated, and even causing the system to shut down whenconditions warrant such action. A flowchart for a method of monitoringand controlling the function of dry gas seals in a compressor during adynamic operating condition is shown in FIG. 6. As shown in theflowchart, the method includes monitoring various operating parametersof the seals and of the seal gas supply system at 602. In oneembodiment, such monitoring includes the interrogation of various sensorsignals provided to the programmable logic controller 324 (FIG. 3), andthe subsequent comparison of each signal with a corresponding acceptablerange and/or maximum permitted value.

More specifically, the programmable logic controller 324 is disposed toreceive various parameters indicative of the conditions of operation ofthe first stage seal 110 and the second stage seal 111 (FIG. 1), whichinclude signals such as the first stage phase signal 170, the firststage seal temperature signal 182, the second stage phase signal 174,the second stage temperature signal 186, the third phase signal 178, andothers. Each of these signals may be compared with a corresponding andpredetermined range of acceptable values, and may be further compared toa corresponding maximum allowable value. Additionally, the programmablelogic controller 324 is disposed to receive signals indicative ofvarious operating parameters of a gas supply system for the dry gasseals operating within a compressor. Such signals may include, as shownin FIG. 2, the pressure signal 231, the temperature signal 233, thepressure difference signal 237, the process gas phase signal 239, thesealing gas temperature 245, the sealing gas flow rate 247, the barriergas inlet flow signal 275, the barrier gas phase signal 277, the barriergas inlet pressure signal 279, the separation gas inlet flow signal 281,the separation gas phase signal 283, the separation gas inlet pressuresignal 285, and others.

These and other signals are monitored at 602 continuously duringoperation of the compressor. The various sensor signals are processed at604 to determine whether indications exist for an anomalous operatingcondition. Such processing of sensor signals may include comparisons ofeach sensor signal with a corresponding acceptable or expected range ofoperation, and may further include a comparison of each sensor signalwith a maximum allowable value. For example, one of the sensor signalsmonitored may be a seal temperature, such as the first stage sealtemperature signal 182 (FIG. 1), and compared with an acceptabletemperature range to determine whether the temperature of the firststage seal 110 (FIG. 1) falls within the acceptable range and whether itexceeds a maximum allowable range.

A determination at 606 is made whether one or more indications of amalfunction or of an anomalous operating condition is/are present. Suchdetermination causes a notification of the condition to the operator oranother output signal to be provided at 608, for example, by activationof an alarm or warning, and in one embodiment further causes theinitiation of a mitigation procedure aimed at correcting the anomaly at610, when a condition is present. For example, one type of anomalousoperating condition that may be determined to exist is a flooding in theprocess that causes fluids to be carried into the first stage and thesecond stage seals.

The determination of when such condition is present, especially in thecase when the seals are operating below the evaporation temperature ofsuch liquid, can be made by the evaluation of various sensor signals. Inthis instance, for example, the primary seal temperature may be belowits nominal operating level, the first stage phase sensor may indicatethe presence of liquid, the second stage seal temperature may be aboveits nominal level, and the second stage seal phase sensor may indicatethe presence of liquid. To mitigate such condition, the control systemmay increase the gas flow through the first and second seals, to flushout the liquid, and increase the temperature of the treated process gasprovided to the first seal, to aid in evaporating any remaining liquid.

Various methods of performing the failure mitigation actions may beemployed. In one exemplary embodiment, the control system may performadjustments to the flow rates and temperatures of the various gasesprovided to the seals by commanding a series of incremental changes tosuch parameters to various components responsible for adjusting suchparameters. For instance, in the example described above, an increase inthe temperature of the treated process gas may be performed according tothe following algorithm:P009(i+1)=P009(i)+dTwhere “P009” is a variable indicative of a commanded temperature of theprocess gas, such as the temperature change command signal 241 (FIG. 2),P009(i) is a temperature command at a given time, P009(i+1) is thetemperature command after a process time or cycle time interval, whichdepends on an execution rate of the control system, and “dT” is atemperature increment value. One can appreciate that the above equationwill cause step increases to the temperature of the process gas witheach execution cycle. Such increase may continue provided thetemperature of the gas remains below the maximum allowable temperature.

For further illustration of the above-mentioned example, the flow rateof the gases supplied to the first and second stage seals may begoverned by the following algorithm:P113/115(i+1)=P113/115(i)+dQwhere “P113/115” is a ratio of the gas flow rate provided to the firststage seal over the gas flow rate provided to the second stage seal,such as the ratio of the flow control signal 243 (FIG. 2) over thebarrier gas valve control signal 271, the ratio being adjusted toprovide a uniform pressure difference across the seals, (i+1) and (i)indicating two consecutive flow commands, and “dQ” is a flow-ratioincrement value.

If the mitigation at 610 is not accomplished before one or moreparameters reaches a maximum permitted value is reached at 612, thecontrol system may activate an additional alarm at 614 and shut-down thesystem at 616 to avoid damage to the equipment. As previously described,such monitoring and control of the operation of dry gas seals in acompressor can be effective in automatically correcting anomalousconditions that may lead to the malfunction and reduction in the servicelife of various seals, by adjusting operating values in the system.Consistent with the exemplary mitigation procedure discussed above, thecontrol system is capable of determining the presence of many otherconditions requiring mitigation, and adjusting other operatingparameters.

A collection of various anomalous operating conditions requiring actionby the control system is presented in Table 1 below, along with thecorresponding actions that may be taken by the control system to rectifysuch conditions. In the table, the anomalous conditions appear innumbered rows 1-18 as combinations of six sensor inputs appearing underthe header “Sensor Signal Information.” The mitigating action for eachcondition appears as a combination of actions under the heading “ControlSystem Action.” In the exemplary collection of data in the table, “F.S.HOT” is indicative of the temperature of the first stage seal exceedinga nominal operating temperature, “F.S. LIQ.” equal to 1 indicates thepresence of liquid at the first stage seal, “S.S. HOT” indicates aheated condition of the second stage seal, and “S.S. LIQ.” indicates thepresence of liquid at the second seal. Similarly, “SYS LIQ.” indicatesthe presence of liquid in the treatment system for the process gas at alocation downstream of the knockout filters, and “VENT OIL” indicatesthe presence of oil from the bearing cavity invading the seals.

An exemplary collection of mitigating acts are also presented in thetable, where “F.S. GAS INCR.” indicates an increase in the flow rate ofgas provided to the first stage seal, “S.S. GAS INCR” indicates anincrease in the flow rate of gas provided to the second stage seal, “GASRATIO INCR.” indicates an increase in the ratio of flow rates of gasesto the first and second stage seals, “SEPARATION GAS INCR.” indicates anincrease in the flow rate of gas provided to the separation seal (forexample, the separation seal 144 shown in FIG. 1), and “TEMP. INCR.”indicates a temperature increase of process gas provided to the firststage seal. Such flow rate or temperature increases may be performed bygradual or incremental increases as described in the example above, ormay be performed by any other suitable fashion, for example, ramp orlinear changes, changes following a functional relationship, and soforth. Table 1 is presented below:

TABLE 1 Control System Action Sensor Signal Information F.S. S.S. GASF.S. F.S. S.S. S.S. SYS. VENT GAS GAS RATIO SEPARATION TEMP. # HOT LIQ.HOT LIQ. LIQ. OIL INCR. INCR INCR. GAS INCR. INCR. 1 YES 1 YES 1 0 0 — —YES — YES 2 YES 1 NO 0 0 0 YES — — — YES 3 YES 1 YES 1 1 0 — YES — — YES4 YES 1 NO 0 1 0 — YES — — YES 5 YES 0 YES 1 0 0 — — YES — YES 6 YES 0NO 0 0 0 — — YES — YES 7 NO 1 YES 1 0 0 — — YES — YES 8 NO 1 NO 0 0 0YES — — — YES 9 NO 1 YES 1 1 0 — YES — — YES 10 NO 1 NO 0 1 0 — YES — —YES 11 NO 0 YES 1 0 0 — — YES — YES 12 NO 0 NO 0 1 1 — YES — YES — 13YES 1 YES 1 0 1 — — YES YES YES 14 YES 1 YES 1 1 1 — YES — YES YES 15YES 0 YES 1 0 1 — — YES YES YES 16 YES 1 YES 1 0 0 — — YES YES YES 17YES 1 YES 1 1 0 — YES — — YES 18 YES 0 YES 1 0 0 — — YES YES YESAs can be seen from the above table, various mitigation measures may betaken. The example involving the presence of liquid in the first andsecond seals discussed above corresponds to row #1 of the table.

The measures shown and described relative to Table 1 may be implementedfor each of multiple seals or sets of seals used in a compressor system.In one embodiment, each of the first and second seals disposed in thedischarge side of a compressor may be monitored and controlled accordingto the above table, and a second set of a first and second seal disposedat the suction end of a compressor may be controlled by a similar,corresponding table within the control system.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

The invention claimed is:
 1. A seal monitoring system for a gaslubricated non-contacting seal assembly, the seal assembly pre-arrangedinto a cartridge and disposed in a seal chamber defined by a housing insealing relationship between a rotatable shaft and said housing, thehousing defining an axially inboard first annular passage, an axiallyoutboard second annular passage, and an axially midboard third annularpassage located axially between the first annular passage and the secondannular passage, the seal assembly having a first stage seal disposedwithin the cartridge, the cartridge and first stage seal defining afirst stage chamber, the first stage chamber and first annular passagedefining a first gas inlet, the seal assembly having a second stage sealdisposed within the cartridge, the cartridge and second stage sealdefining a second stage chamber, the second stage chamber and secondannular passage defining a second gas inlet, the cartridge furtherdefining a leakage chamber, the leakage chamber and the third annularpassage defining a leakage outlet, the first gas inlet receiving a firstgas, at least a portion of the first gas flowing towards the leakageoutlet, the second gas inlet receiving a second gas, at least a portionof the second gas flowing towards the leakage outlet, the sealmonitoring system comprising: a first phase sensor disposed in the firstgas inlet to provide a first phase signal indicative of non-gaseousmatter in the received first gas; a second phase sensor disposed in theleakage outlet to provide a second phase signal indicative ofnon-gaseous matter in the portion of the first gas flowing toward theleakage chamber and the portion of the second gas flowing toward theleakage chamber; and a control system disposed to receive said first andsecond phase signals, wherein said control system is further disposed todetermine an operating condition of said gas lubricated non-contactingseal assembly based on said first and second phase signals and providean output signal in response to said operating condition, the outputsignal enabling early warning and mitigation of one or more potentialanomalous or fault conditions.
 2. The seal monitoring system of claim 1,further comprising a first temperature sensor disposed in said sealchamber to provide a first temperature signal indicative of atemperature of a component of said gas lubricated non-contacting seal,wherein the control system is further disposed to receive said firsttemperature signal and provide said output further based on said firsttemperature signal.
 3. The seal monitoring system of claim 1, whereinthe control system is further disposed to determine a presence of ananomalous operating condition based on said operating condition, andperform at least one mitigating process to correct said anomalousoperating condition by adjusting at least one operating parameter ofsaid gas lubricated non-contacting seal.
 4. The seal monitoring systemof claim 3, further comprising a process gas treatment module arrangedto provide a flow of process gas to said seal assembly, said process gastreatment module including: a process gas conduit adapted to providesaid flow of process gas from an upstream end to a downstream endthereof; at least one coalescing filter fluidly intersecting saidprocess gas conduit; a differential pressure sensor disposed across saidat least one coalescing filter along said process gas conduit andproviding a process gas differential pressure signal; a process gasphase sensor disposed to provide a process gas phase signal indicativeof non-gaseous matter in said process gas conduit downstream of said atleast one coalescing filter; a process gas temperature sensor disposedto provide a process gas temperature signal; a process gas flow sensordisposed to provide a process gas flow signal indicative of a flow rateof said flow of process gas downstream of said at least one coalescingfilter; wherein said control system is further disposed to perform saidat least one mitigating process based on at least one of said processgas differential pressure signal, process gas phase signal, process gastemperature signal, and process gas flow signal.
 5. The seal monitoringsystem of claim 4, wherein said process gas treatment module furthercomprises: a heater/cooler device disposed along said process gasconduit and disposed to adjust a process gas temperature in response toa temperature change command signal provided by said control system; anda flow control device disposed along said process gas conduit anddisposed to adjust a rate of flow of said flow of process gas inresponse to a flow control signal provided by said control system;wherein at least one of said temperature change command signal and saidflow control signal is provided as part of said at least one mitigatingprocess of said control system.
 6. The seal monitoring system of claim1, further comprising a first gap sensor disposed in said seal chamberto provide a first gap signal indicative of a distance between a firstprimary ring and a first mating ring of said gas lubricatednon-contacting seal, wherein the determination of said operatingcondition of said gas lubricated non-contacting seal is further based onsaid first gap signal.
 7. The seal monitoring system of claim 1, furthercomprising a position sensor disposed in said seal chamber to provide aposition signal indicative of an axial distance between one or morerotating parts of said seal and said rotatable shaft and one or morestationary parts of said housing wherein the determination of saidoperating condition of said gas lubricated non-contacting seal isfurther based on said position signal.
 8. The seal monitoring system ofclaim 7, wherein the control system is further disposed to activate anadditional output signal when said position signal indicates that saidaxial distance is beyond and acceptable value.
 9. A seal monitoringsystem for a gas lubricated non-contacting seal assembly disposed in aseal chamber defined by a housing of a compressor, and being in sealingrelationship between a rotatable shaft and said housing, the sealassembly including one or more stationary components and said one ormore rotatable components, one or more rotatable components beingaxially fixed to said rotatable shaft, and said rotatable shaft beingaxially moveable relative to said housing, the seal monitoring systemcomprising: a position sensor disposed in said seal chamber to provide aposition signal indicative of a relative axial position of at least oneof the one or more rotatable components and said housing therebyindicating relative movement between said housing and said shaft; and acontrol system disposed to receive said position signal, wherein saidcontrol system is further disposed to determine an operating conditionof said gas lubricated non-contacting seal assembly based on saidposition signal and provide an output signal in response to saidoperating condition a process gas treatment module arranged to provide aflow of process gas to said gas lubricated non-contacting seal assemblyvia a process gas inlet passage formed in the housing of the compressor,said process gas treatment module including— a process gas conduitadapted to provide said flow of process gas from an upstream end to adownstream end thereof; at least one coalescing filter fluidlyintersecting said process gas conduit; a differential pressure sensordisposed across said at least one coalescing filter along said processgas conduit and providing a process gas differential pressure signal; aprocess gas phase sensor disposed to provide a process gas phase signalindicative of non-gaseous matter in said process gas conduit downstreamof said at least one coalescing filter; a process gas temperature sensordisposed to provide a process gas temperature signal; a process gas flowsensor disposed to provide a process gas flow signal indicative of aflow rate of said flow of process gas downstream of said at least onecoalescing filter; wherein said control system is further disposed toperform said at least one mitigating process based on at least one ofsaid process gas differential pressure signal, process gas phase signal,process gas temperature signal, and process gas flow signal.
 10. Theseal monitoring system of claim 9, wherein said process gas treatmentmodule further comprises: a heater/cooler device disposed along saidprocess gas conduit and disposed to adjust a process gas temperature inresponse to a temperature change command signal provided by said controlsystem; and a flow control device disposed along said process gasconduit and disposed to adjust a rate of flow of said flow of processgas in response to a flow control signal provided by said controlsystem; wherein at least one of said temperature change command signaland said flow control signal is provided as part of said at least onemitigating process of said control system.